1. Field of the Invention
The present invention relates to wireless integrated circuit (IC) tags. More particularly, the present invention relates to a wireless IC tag used in a Radio Frequency Identification (RFID) system, a reader-writer communicating with the wireless IC tag, and an information processing system including the wireless IC tag.
2. Description of the Related Art
Hitherto, Radio Frequency Identification (RFID) systems have been developed as article management systems. In such an RFID system, a reader-writer producing an induction electromagnetic field communicates with a wireless tag in a non-contact manner to transmit information. The wireless tag is attached to an article and stores certain information. A wireless IC tag including two coil-shaped antennas is described in Japanese Unexamined Patent Application Publication No. 2004-126750 as a wireless tag used in an RFID system. The two coil-shaped antennas are connected in series to each other so as to form a figure eight.
However, since the two coil-shaped antennas have opposite winding directions in the wireless IC tag, the wireless IC tag has a disadvantage in that, in response to reception of a high-frequency magnetic field radiated from a loop antenna of the reader-writer, a current occurring in one coil-shaped antenna is offset by a current occurring in the other coil-shaped antenna. Accordingly, there is a problem in that the energy transfer efficiency between the wireless IC tag and the reader-writer is reduced to decrease the communication distance.